1. Field of the Invention
The present invention relates to a rubber-reinforcing aromatic polyamide multifilament yarn. More particularly, the present invention relates to a rubber-reinforcing aromatic polyamide multifilament yarn having an excellent bonding property to rubber materials and a high resistance to fraying of individual filaments.
When a multifilament yarn-reinforced rubber cyclic belt, for example, timing belt or low edge V-belt is produced by cutting in round slices a cylindrical product in which a reinforcing multifilament yarn material (cord) is embedded in a rubber matrix, peripheral faces of the mutifilament yarns are exposed on the cut face of the belt, on this cut face individual filaments are often frayed from the multifilament yarns. The rubber-reinforcing multifilament yarn of the present invention exhibits a high resistance to the fraying of the individual filaments.
2. Description of the Related Art
It is known that aromatic polyamide filaments or fibers generally have excellent mechanical strength, modulus of elasticity, dimensional stability and heat resistance and thus are useful as reinforcing fibers for tires, belts and hoses that are used under hard conditions. The aromatic polyamide filaments, in particular, has a high specific tensile strength and specific modulus of elasticity and therefore are useful as light weight reinforcing filaments, in place of reinforcing steel wires.
Generally, when the aromatic polyamide multifilament yarns are used as reinforcing filaments for a timing belt or low edge V-belt, the belt is produced in such a manner that a cylindrical material in which an aromatic polyamide multifilament yarn is embedded in a rubber matrix is formed, and the cylindrical material is cut in round slices by using a cutter. On the cut faces of the belt, peripheral faces of the multifilament yarns are exposed, and a portion of the individual filaments is frayed from the multifilament yarns and extend from the cut faces of the belt to the outside therefore, thereby causing the quality of the resultant belt to be lowered. Namely, if the belt having the frayed individual filaments is placed on a pulley and subjected to rotation, the frayed individual filaments are abraded by the pulley and divided into fine pieces that are sprinkled around the pulley, or the frayed individual filaments reduces the durability of the belt.
The above-mentioned disadvantages can be eliminated by mechanically removing or cutting the frayed individual filaments from the belt during the belt-producing procedure. This removal operation significantly reduces the productivity of the belt. Accordingly, this disadvantage is a significant barrier against industrially using the aromatic polyamide multifilament yarns as a reinforcing material for rubber material.
To eliminate the above-mentioned disadvantages, Japanese Unexamined Patent Publication Nos. 1-207,480 and 4-29,644 disclose an attempt to prevent the fraying of individual filaments from the aromatic polyamide multifilament yarns by treating the multifilament yarn with a specific treating agent. However, this attempt was not always successful because the treated aromatic polyamide multifilament yarns exhibited a reduced mechanical strength, lowered bonding properties and/or a poor durability.